Method and apparatus of content adaptive detailing filtering for digital pictures

ABSTRACT

According to one embodiment, a method is disclosed. The method includes receiving video data performing pre-filtering on the data, performing content analysis is applied to identify an area of the data, applying a two-dimensional (2-D) 2 nd  gradient operation to extract a high frequency component and normalizing the high frequency component related to high frequency information from a previous picture.

FIELD OF THE INVENTION

The present invention relates to computer systems; more particularly,the present invention relates to video processing.

BACKGROUND

Image enhancement is an important factor in the field of videoprocessing. On the end user side of an image/video application, imageenhancement techniques are typically applied as part of post-processingfiltering to improve picture quality. Conventional media processorsimprove picture quality by magnifying the high frequency component toincrease the detail/sharpness of picture content. Unfortunately,magnifying the high frequency component blindly will lead to undesirablepicture quality due to the magnifying of the noise detail of picturecontent.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example and not limitation in thefigures of the accompanying drawings, in which like references indicatesimilar elements, and in which:

FIG. 1 is a block diagram of one embodiment of a computer system;

FIG. 2 is a flow diagram illustrating one embodiment for performingdetail filtering;

FIG. 3 is a flow diagram illustrating a further embodiment forperforming detail filtering;

FIG. 4 illustrates one embodiment of an equation and location of pixelsfor a high frequency component extraction process for a central targetpixel; and

FIG. 5 illustrates one embodiment of a graph mapping edge detectionversus filtering weighting over conventional edge detection measures.

DETAILED DESCRIPTION

A content adaptive detail filtering mechanism is disclosed. In oneembodiment, the mechanism includes components that are applied to apost-processing system that in the areas of video, image, display andmedia processors. In one embodiment, the components include processes toenhance image/video visual quality by increasing picturedetail/sharpness through content adaptive filtering; provide contentanalysis by utilizing edge detection and noise detection to adapt theuse of detail filtering; provide better/accurate content analysis byutilizing the pre-process filtering to improve edge detection and noisedetection; provide detail filtering by a proposed two-dimensional (2-D)2^(nd) derivative formula to extract high frequency component; providedetail filtering by normalizing the filtering amount by a maximum of ahigh frequency component detected from a previous picture; providedetail filtering by modifying a filtering amount by a noise detection ora portion of the maximum of the high frequency component detected fromthe previous picture; and provide detail filtering by allowing end usersto specify a filtering gain factor to modify a filtering amount toachieve a user preference.

In the following detailed description of the present invention numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be apparent toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in block diagram form, rather than indetail, in order to avoid obscuring the present invention.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the invention. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment.

Some portions of the detailed descriptions that follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

The instructions of the programming language(s) may be executed by oneor more processing devices (e.g., processors, controllers, controlprocessing units (CPUs),

FIG. 1 is a block diagram of one embodiment of a computer system 100.Computer system 100 includes a central processing unit (CPU) 102 coupledto interconnect 105. In one embodiment, CPU 102 is a processor in thePentium® family of processors Pentium® IV processors available fromIntel Corporation of Santa Clara, Calif. Alternatively, other CPUs maybe used. For instance, CPU 102 may be implemented multiple processors,or multiple processor cores.

In a further embodiment, a chipset 107 is also coupled to interconnect105. Chipset 107 may include a memory control component (MC) 110. MC 110may include a memory controller 112 that is coupled to a main systemmemory 115. Main system memory 115 stores data and sequences ofinstructions that are executed by CPU 102 or any other device includedin system 100.

MC 110 may be coupled to an input/output control component (IC) 140 viaa hub interface. IC 140 provides an interface to input/output (I/O)devices within computer system 100. IC 140 may support standard I/Ooperations on I/O interconnects such as peripheral componentinterconnect (PCI), accelerated graphics port (AGP), universal serialinterconnect (USB), low pin count (LPC) interconnect, or any other kindof I/O interconnect (not shown). In one embodiment, ICH 140 is coupledto a wireless transceiver 160.

According to one embodiment, IC 140 includes an instruction set toperform a content adaptive detail filtering of video data. However inother embodiments, IC 140 may include hardware modules to perform theprocess. In further embodiments, CPU 102 may be implemented to performthe process.

FIG. 2 is a flow diagram illustrating one embodiment for performingdetail filtering. At processing block 210, a video input is received. Atprocessing block 220, pre-filtering is performed to smooth a picture. Atprocessing block 230, content analysis is applied to identify an area ofinterest such as edge region. At processing block 240, a 2-D 2^(nd)gradient operation is applied to extract a high frequency component.

At processing block 250, the high frequency component is normalizedrelated to the same high frequency information from a previous picture.At processing block 255, the adjustment amount is refined by a result ofedge detection. At processing block 260, the processed video data istransmitted from ICH 140. The individual processes 220-255 are describedbelow in greater detail.

According to a further embodiment, a parameter setting is provided forusers to select a refinement amount to a user's preference. FIG. 3 is aflow diagram illustrating a further embodiment for performing detailfiltering incorporating user preferences. At processing block 320, amultiplier is applied to the refined value to provide an adjustmentbased upon a gain factor defined by a user. At processing block 325,clipping is performed. In one embodiment, the clipping is based upon thelocal maximum and local minimum of 3×3 neighborhood pixels processedduring detail filtering. At processing block 330, the adjusted value isadded to the video input. At processing block 340, a second clippingoperation is performed prior to forwarding to the video output.

Pre-Filtering

The use of a low pass pre-processor to remove noise improves theaccuracy of picture analysis. According to one embodiment, a 2-Dpre-edge filter is implemented with a weighting w. In a furtherembodiment, the 2-D filter may be decomposed into two 1-D filters toreduce the number of operations. This can be represented as:

$\begin{matrix}\begin{matrix}{{{Pre\_ edge}{\_ filter}{\_ weighting}\mspace{14mu} w} = \begin{bmatrix}1 & 2 & 1 \\2 & 4 & 2 \\1 & 2 & 1\end{bmatrix}} \\{= {\begin{bmatrix}1 \\2 \\1\end{bmatrix}*\left\lbrack {1\mspace{14mu} 2\mspace{14mu} 1} \right\rbrack}}\end{matrix} & \lbrack 1\rbrack\end{matrix}$

Considering a target pixel x with 3×3 neighborhood pixels, NH9(x), theoutput of the pre-edge-filter is represented by:

$\begin{matrix}{{{pre\_ edge}{\_ filter}{\_ output}} = {\left( \frac{1}{\sum\limits_{x \in {{NH}\; 9{(x)}}}{w(x)}} \right) \cdot \left( {{\sum\limits_{x \in {{NH}\; 9{(x)}}}{{w(x)} \cdot x}} + {{1/2} \cdot {\sum\limits_{x \in {{NH}\; 9{(x)}}}{w(x)}}}} \right)}} & \lbrack 2\rbrack\end{matrix}$

In Equation 2 above, the Σw(x)=16 for the summation of thepre_edge_filter_weighting in the Equation 1. The last term, ½·Σw(x), isused for the rounding purpose. The above formula is included in thisembodiment due to the simply complexity. However in other embodiments,other pre-processor techniques may be applied.

Content Analysis—Edge Protection

According to one embodiment, edge detection is used as the contentanalysis process to identify a pixel of interest to be applied fordetail filtering. In such an embodiment, a Sobel edge operator, shownbelow, is applied as the edge detection process in four directions.

$\begin{matrix}{{{E\_ h} = \begin{bmatrix}{- 1} & {- 2} & {- 1} \\0 & 0 & 0 \\1 & 2 & 1\end{bmatrix}}{{E\_ v} = \begin{bmatrix}{- 1} & 0 & 1 \\{- 2} & 0 & 2 \\{- 1} & 0 & 1\end{bmatrix}}{{{E\_ P}\; 45} = \begin{bmatrix}{- 2} & {- 1} & 0 \\{- 1} & 0 & 1 \\0 & 1 & 2\end{bmatrix}}{{{E\_ N}\; 45} = \begin{bmatrix}0 & {- 1} & {- 2} \\1 & 0 & {- 1} \\2 & 1 & 0\end{bmatrix}}} & \lbrack 3\rbrack\end{matrix}$

The edge metric (EM) for the target pixel x is formulated as theconvolution of the weighting in the Equation 3 with its 3×3 neighborhoodNH9(x) asEM(x)=|NH9(x)*E _(—) h|+|NH9(x)*E _(—) v|=|NH9(x)*E _(—) P45|+|NH9(x)*E_(—) N45|  [4]

According to one embodiment, the use of two directions, (e.g., E_v, andE_h) may be sufficient for most applications. The detection at 45degrees further improves the edge detection with more computationalcomplexity.

High Frequency Component Extraction

In one embodiment, the 2-D formula shown above in Equation 5 is used toextract the high frequency component. FIG. 4 illustrates the highfrequency component. As shown in FIG. 4, the high frequency component isdenoted as the sigma for the central pixel Xc

$\begin{matrix}{{2{nd\_ gradient}} = \begin{bmatrix}{- 1} & 0 & {- 1} & 0 & {- 1} \\0 & 0 & 0 & 0 & 0 \\{- 1} & 0 & 8 & 0 & {- 1} \\0 & 0 & 0 & 0 & 0 \\{- 1} & 0 & {- 1} & 0 & {- 1}\end{bmatrix}} & \lbrack 5\rbrack\end{matrix}$Refinement

The refinement process includes two modification processes:normalization & edge adaptive. In one embodiment, the Sigma(Xc) isnormalized by the maximum of the sigma value of the previous picture,sigma_max_previous, such that:Temp_sigma(Xc)=C*(sigma(Xc)/sigma_max_previous−delta)  [7]

In one embodiment, the parameter C, which may be specified by users, isa weighting coming from the edge detection. In such an embodiment,pixels are classified as being a strong edge pixel, weak edge pixel andnon-edge pixel. Subsequently, the C value is assigned according to theedgeness property of the pixel. FIG. 5 illustrates one embodiment of agraph mapping edge detection versus filtering weighting overconventional edge detection measures. As shown in FIG. 5, the low edgepixels are not modified by the high frequency measure.

The delta in Equation 7 is a threshold to the high frequency componentextraction above in which the modification is added to reconstruction.In one embodiment, this process is set by a noise detection level.However, such a process is not described herein so as not to provideconfusion as to the scope of this invention. Thus, in this embodiment,10% of sigma_max_previous is used as the threshold value.

User Preferences

As discussed above, may be provided by allowing end users to specify afiltering gain factor to modify a filtering amount to achieve a userpreference. In such an embodiment, the amount of adjustment results in afinal adjustment that is represented in Equation 8 as:Final_sigma(Xc)=K*Temp_sigma(Xc)  [8]

In one embodiment, the parameter K is a constant selected by a user.Further, represented in Equation 9 as:Output(Xc)=clipping(Xc+Final_sigma(Xc)  [9]

-   -   Where clipping(x)=255 if x>255, clipping(x)=0 if x<0, otherwise,        clipping(x)=x.

The above-described mechanism achieves improved picture quality byutilizing the local spatial content information with the edge detectionto adapt high frequency component adjustment to provide gracefulenhancement of picture detail. Further, the pre-filtering processextracts more reliable high frequency components and more accuratecontent analysis. In addition, an effective high frequency componentextraction clipping is applied to avoid underflow or overflow inproducing the output process implements a two-Dimensional 2^(nd)derivative formula to filter out the high frequency component toillustrate the detail of picture. Moreover, users are permitted toconfigure for various applications by allowing the user to specify again factor to achieve a user desirable viewing experience.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims, which in themselves recite only those features regarded asessential to the invention.

1. A method comprising: receiving video data; performing pre-filteringon the data; performing content analysis to identify an area of thedata; applying a two-dimensional (2-D) 2^(nd) gradient operation toextract a high frequency component; and normalizing the high frequencycomponent related to high frequency information from a previous picture.2. The method of claim 1 further comprising receiving one or more userdefined parameters to provide detail filtering to achieve a userpreference.
 3. The method of claim 2 wherein the user defined parametersinclude a filtering gain factor.
 4. The method of claim 1 whereinperforming the pre-filtering comprises using a 2-D filter to removenoise from the data.
 5. The method of claim 4 wherein the 2-D filter isdecomposed into two 1-D filters to reduce a number of operations.
 6. Themethod of claim 1 wherein performing content analysis comprises using anedge detection operation to identify a pixel of interest to be appliedfor detail filtering.
 7. The method of claim 6 wherein the edgedetection operation is a Sobel edge operation.
 8. The method of claim 1wherein normalizing the high frequency component comprises using an edgeadaptive modification process.
 9. The method of claim 8 wherein the edgeadaptive modification process classifies pixel data as strong edgepixels, weak edge pixels and non-edge pixels.
 10. A processorcomprising: a component to receive video data; a component to performpre-filtering on the data; a component to perform content analysis toidentify an area of the data; a component to apply a two-dimensional(2-D) 2^(nd) gradient operation to extract a high frequency component;and a component to normalize the high frequency component related tohigh frequency information from a previous picture.
 11. The processor ofclaim 10 further comprising a component to receive one or more userdefined parameters to provide detail filtering to achieve a userpreference.
 12. The processor of claim 11 wherein the user definedparameters include a filtering gain factor.
 13. The processor of claim10 wherein the component to perform pre-filtering comprises a 2-D filterto remove noise from the data.
 14. The processor of claim 13 wherein the2-D filter is decomposed into two 1-D filters to reduce a number ofoperations.
 15. The processor of claim 10 wherein the component toperform content analysis comprises an edge detection operation toidentify a pixel of interest to be applied for detail filtering.
 16. Theprocessor of claim 10 wherein the component to normalize comprises anedge adaptive modification process to classify pixel data as strong edgepixels, weak edge pixels and non-edge pixels.
 17. An article ofmanufacture including one or more computer readable media that embody aprogram of instructions, wherein the program of instructions, whenexecuted by a processing unit, causes the processing unit to perform theprocess of: receiving video data; performing pre-filtering on the data;performing content analysis to identify an area of the data; applying atwo-dimensional (2-D) 2^(nd) gradient operation to extract a highfrequency component; and normalizing the high frequency componentrelated to high frequency information from a previous picture.
 18. Thearticle of manufacture of claim 17 wherein when executed by a processingunit, further causes the processing unit to perform the process ofreceiving one or more user defined parameters to provide detailfiltering to achieve a user preference.
 19. The method of claim 18wherein the user defined parameters includes a filtering gain factor.20. A system comprising: a central processing unit; a chipset having: acomponent to receive video data; a component to perform pre-filtering onthe data; a component to perform content analysis to identify an area ofthe data; a component to apply a two-dimensional (2-D) 2^(nd) gradientoperation to extract a high frequency component; and a component tonormalize the high frequency component related to high frequencyinformation from a previous picture; and a wireless transceiver coupledto the chipset.
 21. The system of claim 20 further comprising acomponent to receive one or more user defined parameters to providedetail filtering to achieve a user preference.
 22. The system of claim21 wherein the component to normalize comprises an edge adaptivemodification process to classify pixel data as strong edge pixels, weakedge pixels and non-edge pixels.